Modern telecommunications networks transport an enormous amount of information. Current optical networks are already capable of transporting 100 channels on a single optical fiber, where each channel can carry 40 gigabits per second. Since companies, government agencies, and the military are dependent on receiving uninterrupted service, instantaneous service restoration in the event of link or node failures has become critically important. Even service interruptions for small durations may cause significant disruptions to the exchange of information and may lead to significant financial losses and to inability of executing mission critical tasks.
This invention focuses on optical networks where almost instantaneous restoration in the event of network failures is critically important. Providing dedicated restoration capacity to each of the demands would provide adequate protection, but would be prohibitively expensive. Numerous papers discuss providing protection through variants of shared mesh restoration methods where restoration capacity can be shared by multiple demands with diverse working routes (i.e., with diverse original provisioned routes); for example, the paper by J. Kennington, E. Olinick, A. Ortynski, and G. Spiride, “Wavelength Routing and Assignment in a Survivable WDM Mesh Network”, Operations Research 51, 67-79, 2003. Shared mesh restoration methods use restoration capacity efficiently at the expense of requiring switching and wavelength conversions along intermediate nodes of restoration routes. Furthermore, these methods may require extensive real-time quality testing of end-to-end restoration routes in order to guarantee adequate transmission integrity. Therefore, meeting stringent restoration time requirements for end-to-end restoration routes with adequate quality may be quite challenging.
Preconfigured restoration methods that do not require intermediate switching and wavelength conversions along restoration routes are a topic of considerable research for optical networks. The challenge is to design preconfigured restoration capacity that can be shared by various demands in the event of a failure; thus, achieving almost instantaneous, reliable restoration, while still using much less restoration capacity than dedicated restoration routes. It should be noted that ring architectures have been widely used for Synchronous Optical Networks (SONET) and for Wavelength Division Multiplexing (WDM) networks; see, for example, the paper by S. Cosares, D N. Deutsch, I. Saniee, and O. J. Wasem, “SONET Toolkit: A Decision Support System for Designing Robust and Cost-effective Fiber-optics Networks”, INTERFACES 25, No. 1, 20-40, 1995. The resulting networks consist of multiple interconnecting rings where both the demands' working routes and their respective restoration routes are restricted to use only the rings. Local demand may use only a single ring while long distance demands may be routed through multiple interconnected rings. This architecture guarantees very fast and reliable restoration at the expense of significant infrastructure capacity since, typically, working routes restricted to rings are significantly longer than the shortest possible routes and half of the ring capacities is reserved for restoration.
Combining the advantages of arbitrary, often referred to as mesh, working routes with preconfigured restoration methods that allow for capacity sharing without resorting to intermediate switching and wavelength conversions on restoration routes seems to be an attractive approach. A. Kodian and W. D. Grover, “Failure-Independent Path-Protecting p-Cycles: Efficient and Simple Fully Preconnected Optimal-Path Protection”, Journal of Lightwave Technology 23, 3241-3259, 2005, A. Kodian, W. D. Grover, and J. Doucette, “A Disjoint Rout-Sets Approach to Design of Path-Protecting p-Cycle Networks”, Proceedings of Workshop on Design of Reliable Communication Networks (DRCN 2005), 231-238, Naples, Italy, October 2005, and D. Baloukov, W. D. Grover, and A. Kodian, “Toward Jointly Optimized Design of Failure-Independent Path Protecting p-Cycle Networks”, Journal of Optical Networking 7, 62-79, 2008, present a method for mesh working routes of the demands, where end-to-end restoration routes are provided on preconfigured cycles. In their method, referred to as the Failure Independent Path Protecting (FIPP) p-cycles method, multiple demands that do not have any common failure scenarios can be protected by the same cycle. However, their method does not support the assignment of demands with common failure scenarios on the same cycle. Furthermore, their method allows splitting restoration for multiple-wavelength demands across multiple routes in the same or different cycles.
T. Y. Chow, F. Chudak, and A. M. Ffrench, “Fast Optical Layer Mesh Protection Using Pre-Cross-Connected Trails”, IEEE/ACM Transactions on Networking 12, 539-548, 2004, present a method that protects mesh working routes of the demands on restoration routes, referred to as trails, that are not constrained to be on cycles but are flexible to follow other structures such as paths with or without loops. Their method allows the sharing of restoration capacity of a trail by multiple demands that do not have any common failure scenario. Their method assigns one demand at a time, thus, constructing trails sequentially. Hence, the resulting design of trails depends on the order in which the demands are assigned. A. Grue and W. D. Grover, “Improved Method for Survivable Network Design Based on Pre-Cross-Connected Trails”, Journal of Optical Networking 6, 200-216, 2007, applied their FIPP p-cycles method to designing trails for restoration. Again, a trail can support only demands with no common failure scenario and restoration routes of a demand may be split among multiple trails.
H. Luss and R. T. Wong, “Survivable Telecommunications Network Design Under Different Types of Failures”, IEEE Transactions—SMC, Part A: Systems and Humans 34, 521-530, 2004, propose a method that constructs a single cycle that includes all end-nodes of the mesh routes of the demands. Restoration routes for all demands are constructed on the cycle using a pre-specified rule, such as using the shortest route on the cycle. Note that using a single cycle for restoring all demands may lead to inefficient use of capacity due to long restoration routes and the need to protect all demands on that cycle. The method was invented primarily for logical networks (e.g., IP-MPLS); in optical networks a single restoration cycle that includes all end-nodes of the demands may not even exist. Also, the method provides only restoration routes, but does not address the issue of wavelength assignments which is critical when demands that have common failures are assigned to the same cycle.
The present invention provides end-to-end path protection for demands with mesh routes in the network. Restoration routes are provided on segments of cycles where the end-nodes of a working route are the end-nodes of the restoration route for the corresponding demand on the cycle. The method allows multiple demands to share restoration capacity. These demands include those with no common failure scenarios as well as selective demands that do have common failure scenarios, thus achieving more effective use, of restoration capacity than previous methods. Also, the method provides a single restoration route for each of the demands which is often desired by users of optical networks as it simplifies considerable management of traffic at the end-nodes. Nevertheless, the method can readily be modified to allow for multiple restoration routes per demand.